1. Field of Invention
The present invention generally relates to a wireless power transmitter, a wireless power receiver and a control method thereof, and more particularly, to a wireless power transmitter capable of wirelessly transmitting charging power, a wireless power receiver capable of wirelessly receiving charging power, and a control method thereof.
2. Description of the Related Art
Mobile terminals such as cellular phones and Personal Digital Assistants (PDAs) are powered by a rechargeable battery due to their portability. In order to charge the battery, electrical energy may be supplied to the battery of the mobile terminal using a separate charging device. Typically, the charging device and the battery have separate contact terminals mounted on their exposed surfaces, and the charging device and the battery may be electrically connected by causing their contact terminals to be in contact with each other.
However, this contact type charging scheme is subject to contamination due to foreign matter since the contact terminals are exposed to the outside, so the battery charging may not be correctly performed. The battery also may not be correctly charged when the contact terminals are exposed to moisture.
In order to solve these and other problems, wireless or non-contact charging technology has recently been developed and utilized in many electronic devices.
The wireless charging technology, which is based on wireless power transmission/reception, may ensure a system in which a battery may be automatically charged by simply placing, for example, a cellular phone on a charging pad without connecting the cellular phone to a separate charging connector. Typically, wireless electronic toothbrushes or cordless electric shavers are well known as devices employing wireless charging technology. The wireless charging technology may improve the waterproof performance of electronic products by wirelessly charging the electronic products, and may ensure the portability of electronic devices because of the unnecessity of a wired charger. In the coming era of electric vehicles, the related technologies are expected to significantly evolve.
The wireless charging technology may be roughly classified into a coil-based electromagnetic induction scheme, a resonance scheme, and Radio Frequency (RF)/micro wave radiation scheme that converts electrical energy into microwaves and transfers the microwaves.
Up to now, the electromagnetic induction scheme has been widely used. However, as experiments of wirelessly transmitting power from a distance of tens of meters using microwaves have been recently successful at home and abroad, it seems that all electronic products may be wirelessly charged without wires anytime anyplace in the near future.
The electromagnetic induction-based power transmission method corresponds to a scheme of transmitting power between a primary coil and a secondary coil. If a magnet moves around a coil, an induced current may be generated. Based on this principle, a transmitter generates a magnetic field, and a current is induced in a receiver due to a change in the magnetic field, creating energy. This phenomenon is called an electromagnetic induction phenomenon, and a power transmission method employing this phenomenon is excellent in energy transmission efficiency.
As for the resonance scheme, electricity is wirelessly transferred by using the resonance-based power transmission principle as a coupled mode theory even if an electronic device is apart from a charging device by several meters. The wireless charging system causes electromagnetic waves containing electrical energy to resonate, and the resonating electrical energy may be directly transferred only to an electronic device having the resonant frequency. The unused electrical energy may be reabsorbed as an electromagnetic field instead of spreading in the air, so the resonating electrical energy, unlike other electromagnetic waves, may not affect the nearby devices or human bodies.
Although research has recently been conducted on the wireless charging scheme, no standards have been proposed for wireless charging priority, search for a wireless power transmitter and a wireless power receiver, selection of a frequency for communication between a wireless power transmitter and a wireless power receiver, adjustment of wireless power, selection of a matching circuit, distribution of communication time for each wireless power receiver in one charging cycle, and the like. In particular, there is a need for a standard for the configuration and procedure in which a wireless power receiver selects a wireless power transmitter from which the wireless power receiver will receive wireless power.
In particular, there is a need to develop a method in which during discharge of its battery, a wireless power receiver may perform communication with a wireless power transmitter by receiving charging power from the wireless power transmitter. The wireless power receiver may store a stack for communication in its Application Processor (AP), and may load the stack from the AP and communicate with the wireless power transmitter in a process of performing communication with the wireless power transmitter.
However, if its battery is discharged, the wireless power receiver may not load the stack from the AP, so communication for wireless charging may not be performed.